One of the shortcomings of the Petri dish is that there is no control over the biological or physical characteristics of the air or gas that gets into or out of the Petri dish. Ventilation in a Petri dish is often a desirable feature and is presently provided by the "beading" of the rim of the container section if the dish is made of glass and by the presence of "ridges" (usually three) either on the cover at its circumference on the inside or on the rim of container section. These "ridges" or "protrusions" will ensure the presence of a space or a physical gap between the container section and the cover. This gap, however, is big enough to allow not only dust and suspended particulate matter (occasionally) dangerous material e.g. spores of pathogenic fungi to get in (or out) of the plate but also relatively large insects as well e.g. flies and even mites and small roaches to creep freely in and out.
The second disadvantage of this structural deficiency of Petri dishes is that culture media and other relatively volatile constituents dry or dessicate fairly rapidly. Hence, culture of micro-organisms which grow slowly such as Mycobacteria e.g. T.B. and Fungi e.g. Dermatophytes and Dimorphic Fungi are endangered by the rapidly decreasing water content of the culture medium i.e. the medium dries out.
It has been difficult to store cultures on agar plates except for a limited time and the convenience such stored cultures may offer is thereby lost. The same is true for unused media i.e. they cannot be stored for a long time. It is quite evident, then, that with presently known devices, there can be little or practically no control over the gas entering or that may be coming out of a Petri dish or its contents.
There is a definite flow of air in and out of a Petri dish culture as explained by the simple law of gas expansion and shrinkage under varying temperature conditions. Culture media are usually stored at low refrigerator temperatures and have to be warmed when cultures are made. This inevitably entails the expansion of air from inside the plate to the outside. When the plates are removed from the warm temperature of the incubator to be examined at cooler room temperature, the air in the plate has to shrink inviting air from outside into the plate. All these air "movements" happen on account of change in conditions of a purely physical nature (i.e. temperature changes). On the other hand, cultures of microorganisms many of which very actively absorb and/or produce gases generate a relentless fairly strong (sometimes with great force e.g. stormy fermentation by Clostridium welchii) flow of gases in and out of the culture plates. For example, oxygen goes in and carbon dioxide and sometimes hydrogen sulfide go out.